The present invention relates to a high-frequency circuit having a built-in dielectric resonator and a oscillator using this high-frequency circuit, and their production method.
In a frequency processing circuit for the high-frequency region such as microwave and extremely high frequency wave, it is required to reduce the phase noise in order to stabilize the frequency characteristic of the oscillator. In addition, it is effective to increase the load Q factor of the oscillator in order to reduce the phase noise. For example, increasing the Q factor ten times can reduce the phase noise by {fraction (1/100)}.
Thus, using an dielectric material having a high Q factor for the material of the oscillator and shaping precisely the oscillator so as to have a desired resonant frequency, the adhesive agent with a low dielectric constant and a low dielectric loss is coated on another substrate so as to establish the electro-magnetic coupling of the resonator to the micro-strip transmission line formed on the surface connected to the oscillation part in high-frequency mode, or to the micro-strip transmission line formed on the surface of another substrate connected to the oscillation part in high-frequency mode, and then, the resonator is mounted precisely on the surface of another substrate by the precision mounter.
This kind of technology is disclosed, for example, xe2x80x9cMillimeter-wave DRO with Excellent Temperature Stability of Frequencyxe2x80x9d in European Microwave Conferencexe2x80x94Munich 1999, pp.197-200, and xe2x80x9cA novel millimeter-wave multiplayer IC with planer TE010 mode dielectric resonatorxe2x80x9d in 1998 Asia-Pacific Microwave Conference, pp. 147-150.
As disclosed in Japanese Patent Laid-Open Number 10-31219 (1998), Microwave Monolithic Integrated Circuit having a built-in dielectric resonator is known. This is known as such a method that the resonator formed with a high Q factor dielectric material is embedded into the concave part formed on the surface of the substrate of the high-frequency integrated circuit.
In the prior art of the adhesive bonding method in which the resonator is bonded to the micro-strip transmission line connected to the oscillation part so as to establish the electromagnetic coupling, there is such a problem that it is difficult to determine the shape of the resonator and its relative position to the micro-strip transmission line in order to satisfy the desired frequency and power as well as the designated phase noise.
As it is required that the precision for the geometrical dimension of the resonator to its designed target value is xc2x10.1% and that the precision for fixing the resonator to its designed position is xc2x15% of its geometrical dimension, as for the shape, it is necessary to trim the shape of the resonator by grinding the dielectric material, and as for the positioning, it is necessary to mount the resonator by the high-precision mounter, and thus, it has been difficult to operate the mass production and downsize the cost in production.
In the method disclosed in Japanese Patent Laid-Open Number 10-93219 (1998), as the device has such a structure as the integrated circuit, that is, MMIC accommodates the resonator, the size of MMIC is required to be larger than the size of the resonator. However, as the price per unit area of the materials such as GaAs used conventionally as the integrated circuit substrate in the high-frequency region is extremely high, it is difficult to produce the low-cost MMIC. In addition, as the dielectric constant in GaAs substrates is high as in about 13, its dielectric loss gets larger for the oscillator in which the resonator is embedded in the center of the substrate. In this case, as the Q factor as the oscillator is reduced due to the dielectric loss even in the fact of using the dielectric material with high Q factor for the resonator, there is such a problem that the expected effect of high Q factor is not attained.
An object of the present invention is to provide a mounting structure and a production method for the high-frequency semiconductor device which enables an easy and low cost production of the high-frequency circuit in which the trimming of the shape of the dielectric material by grinding work is not required and the relative position between the dielectric material and the high-frequency transmission line can be fixed in a good condition.
In order to attain the above object, in this embodiment, in a high-frequency circuit having a substrate having a high-frequency transmission line and an dielectric resonator formed on said substrate, said substrate has a hole part or a cavity part formed at the position in which said dielectric resonator and said high-frequency transmission line are coupled electro-magnetically to each other, and said dielectric resonator is embedded in said hole part or said cavity part.
Another aspect of the present invention is an oscillator using an external resonator, in which said external resonator has a substrate having a high-frequency transmission line and an dielectric resonator formed on said substrate so as to be coupled electro-magnetically to said high-frequency transmission line;
said substrate is formed by laminating a first dielectric layer and a second dielectric layer, both composed of low-dielectric constant, and said dielectric resonator is composed by using a dielectric material having a dielectric constant higher than a dielectric constant of a dielectric material of said substrate; and
GND layer is formed on one surface of said first dielectric layer and said high-frequency transmission line is formed on the other surface of said first dielectric layer, and said second dielectric layer has said hole part formed at a position suited for making said dielectric resonator coupled electro-magnetically to said high-frequency resonator.
Another aspect of the present invention is an oscillator using an external resonator, in which and said dielectric resonator is composed by using a dielectric material having a dielectric constant higher than a dielectric constant of a dielectric material of said substrate;
said substrate is formed by laminating the first dielectric layer and the second dielectric layer, both composed of low-dielectric constant;
in the external resonator, said second dielectric layer is laminated on said first dielectric layer, a part of said first dielectric layer extends in the side direction to said second dielectric layer, and the first micro-strip transmission line formed in said first dielectric layer is exposed above the surface of said first dielectric layer; and
said first micro-strip layer is converted into the first coplanar transmission line by the conversion part, and MMIC defining said oscillator forms the second coplanar transmission line.
Another aspect of the present invention is a production method of the high-frequency semiconductor device having a substrate having a high-frequency transmission line and a dielectric resonator embedded in said substrate so as to be coupled electro-magnetically to said high-frequency transmission line, comprising a step for forming said high-frequency transmission line on said substrate composed of a dielectric material, a step for forming a hole part or a cavity part partially at a designated position on said substrate suitable for making said dielectric resonator coupling electro-magnetically to said high-frequency transmission line, and a step for mounting said dielectric resonator into said hole part or said cavity part.
Another aspect of the present invention is a method for forming said dielectric resonator, in which said substrate is produced by printing method or lamination method, and furthermore, said hole part or said cavity part is formed in an dielectric layer forming said substrate by using a mask or a cutting die, and a solid solution of dielectric material having a dielectric constant higher than that of the dielectric material used in said substrate is printed and burned on said hole part or said cavity part.
Yet another aspect of the present invention is a method for forming said dielectric resonator, in which said hole part or said cavity part is formed in an dielectric layer forming said substrate by using a mask or a cutting die, an adhesive agent is made coated on said hole part or said cavity part, and the dielectric resonator having a dielectric constant higher than that of the dielectric material used in said substrate, followed by hardening process of said adhesive agent.
According to the present invention, it will be appreciated that a high-precision positioning between the dielectric resonator and the high-frequency transmission line can be made easier, and that high-performance oscillators having a stable frequency characteristic can be produced at a low price.